Cosmic Magnetic Lenses

Magnetic fields play a critical role in the propagation of charged cosmic rays. Particular field configurations supported by different astrophysical objects may be observable in cosmic ray maps. We consider a simple configuration, a constant azimuthal field in a disk-like object, that we identify as a cosmic magnetic lens. Such configuration is typical in most spiral galaxies, and we assume that it can also appear at smaller or larger scales. We show that the magnetic lens deflects cosmic rays in a regular geometrical pattern, very much like a gravitational lens deflects light but with some interesting differences. In particular, the lens acts effectively only in a definite region of the cosmic-ray spectrum, and it can be convergent or divergent depending on the (clockwise or counterclockwise) direction of the magnetic field and the (positive or negative) electric charge of the cosmic ray. We find that the image of a point-like monochromatic source may be one, two or four points depending on the relative position of source, observer and center of the lens. For a perfect alignment and a lens in the orthogonal plane the image becomes a ring. We also show that the presence of a lens could introduce low-scale fluctuations and matter-antimatter asymmetries in the fluxes from distant sources. The concept of cosmic magnetic lens that we introduce here may be useful in the interpretation of possible patterns observed in the cosmic ray flux at different energies.

💡 Research Summary

This paper delves into the critical role of magnetic fields in the propagation of charged cosmic rays. It introduces a concept called “cosmic magnetic lens,” which is characterized by a constant azimuthal field configuration within a disk-like astrophysical object, typical in most spiral galaxies and potentially observable at various scales. The analysis shows that this magnetic lens deflects cosmic rays into regular geometric patterns, similar to how gravitational lenses bend light, but with distinct differences. Specifically, the effectiveness of the lens is confined to specific regions of the cosmic-ray spectrum, and its behavior (converging or diverging) depends on both the direction of the magnetic field (clockwise or counterclockwise) and the charge of the cosmic ray (positive or negative). The paper finds that a point-like monochromatic source can produce one, two, or four images depending on the relative positions of the source, observer, and lens center. In perfect alignment with the observer and lens in orthogonal planes, the image forms a ring. Additionally, the presence of such a magnetic lens could introduce small-scale fluctuations and matter-antimatter asymmetries in fluxes from distant sources. The concept of cosmic magnetic lenses provides new insights into interpreting potential patterns observed in cosmic ray flux at different energies.